Today’s announcement fleshes out some of the key decisions that the Mozilla team has made in the past month.

According to Bondy, Firefox for Metro will mimic Internet Explorer 10’s split personality, as a “Metro style enabled desktop browser”:

Unlike Metro applications, Metro style enabled desktop browsers have the ability to run outside of the Metro sandbox. Meaning not only can we build a browser, but we can build a powerful browser which gives an experience equal to that of a classic Desktop browser.

Metro style enabled desktop browsers have access to most Win32 API and the entire new WinRT API.

Unfortunately a browser can only participate in Metro mode if it is the default browser. So if Firefox is not the default browser on a system, you can't use it in Metro mode. This is a decision made by Microsoft.

Bondy notes that development is in its very early stages, and because of the amount of new code involved it will be “a very large project.” It's too early to even think about UI/UX issues, Bondy acknowledges.

So how long will it take to Metro-ize Firefox? That’s nearly impossible to say. The unique requirements of a desktop enabled browser make development resources difficult to find. It’s not likely that Microsoft is going to be an eager development partner, either. The new Firefox is intended to be a direct competitor to Internet Explorer, and in December Mozilla signed a long-term search deal with Microsoft’s archrival Google.

The Mozilla Wiki topic for Windows 8 says Firefox 14 is the release target date. On Mozilla's new rapid-release schedule, that date is only about four months away, with a public release scheduled for July 17. Given the uncertainties in development and the fluid state of Windows 8, it’s hard to think of that date as much more than a guess, and an optimistic one based on a best-case scenario to boot.

Update: In the Talkback section below, Asa Dotzler clarifies the possible release schedule: "the Firefox 14 target is not a final release of Firefox for Metro. We're working in stages. We have a proof of concept now. Next we'll get an actual browser standing up. After that, an Alpha, then a Beta, then a final release. I do not anticipate that we will get beyond a late stage Beta this year."

[I]f we do our job, Firefox on Windows 8 Metro should be every bit as capable and integrated with the system as Internet Explorer.

Microsoft had an awful big head start with IE 10 but now that we know what's possible, we hope to close that gap.

If you want to track the progress of the project, you can do so via Bug 732518, which was opened a week ago. Yesterday’s report says “So we have a working metro enabled browser application (not an actual browser yet)…”

Clearly, this development effort is a big stake in the ground as Mozilla fights off a relentless assault on its “alternative to IE” status from Google Chrome. If Google decides to jump into the mix as well, the game would change completely.